It’s what happens when the chicken crosses the road, when you hear ‘Mummy, Mummy’, or meet shaggy dogs, blondes, Confucius, or three men entering a bar (metajoke: A priest, a rabbi and a minister walk into a bar, and the bartender says: ‘What is this, a joke?’) – and it’s what started out as an essay on humour for the New Yorker, and has turned into this snappily titled little volume by Jim Holt, quondam American correspondent for LR and devotee of the late Auberon Waugh, who would surely have delighted in the entire undertaking, from its subversive scholarship right down to the Scriblerian index.